1. Field of the Invention
The present invention relates to an optical information recording method and an optical information recording medium containing information recorded by the optical information recording method.
2. Description of Related Art
In an optical information recording medium (recordable optical recording medium), such as a DVD-R or DVD-RW, information is recorded by forming pits.
In information recording, submicron-order pits generated by thermal recording need to be recorded with high accuracy. Therefore, laser pulse control, called a “write strategy” (or, “recording strategy”), is employed for recording the pits. The recording strategy has various functions. In one example, when forming a pit with continual power application corresponding to the length of the pit, the strategy corrects an undesirably long pit resulting from residual heat of a laser beam. In another example, the strategy corrects pit-length nonuniformity caused by signal combination and/or differences in characteristics of the recording layers. In short, the recording strategy is carried out so that proper signals can be reproduced in a replay operation.
As shown in FIG. 5, pit-forming portion P is, for example in an 8T signal, formed such that a front edge is 1T or more behind the rise of recording data (recording signal), and is formed of a top pulse having a relatively large pulsewidth and five multipulses each having a pulsewidth narrower than the top pulse. That is, a write pulse is generally thus formed.
The recording strategy described above is suitably used in optical-information recording for a medium such as a DVD. However, problems arise with the recording strategies in terms of their adaptability to a high-recording-density optical information recording medium that has track pitches narrower than a DVD. Specifically, when the recording strategy is applied to such a high-recording-density optical information recording medium as described above, desired recording pits are less likely to be formed and deterioration in recording characteristics, such as increase in jitter, is observed.